People, I have data DBit = Bit0 | Bit1 deriving (Eq, Ord, Enum) data BNatural = BNat [DBit] deriving (Eq) and want to apply things like fmap reverse (bn :: BNatural). GHC reports an error on this usage of fmap. It also does not allow instance Functor BNatural where fmap f (BNat ds) = BNat $ f ds, -- it reports that a type constructor for Functor must have kind * -> *. Probaly, GHC agrees with Haskell at this point (?). Now, I deceive the compiler by declaring instead newtype BNatAux a = BNat a deriving (Eq) type BNatural = BNatAux [DBit] instance Functor BNatAux where fmap f (BNat ds) = BNat $ f ds So, a parasitic BNatAux is introduced. I wonder: is there a simpler way to have fmap for BNatural ? Thank you in advance for advice, ----------------- Serge Mechveliani mechvel@botik.ru